Is there a way to check which CSS styles are being used or not used on a web page?

Question

Want to know which CSS styles are currently being used on a web page.

Answer 1

Just for completeness and because it was asked in the comments - there's also the CSS audit tool in Chrome now for the same purpose. Some details here:

http://meeech.amihod.com/very-useful-find-unused-css-rules-with-google